Mistakes this n00b made and their solutions

As I'm really starting to map now, I'm also starting to make mistakes. Probably experienced users don't make those (anymore), so there is little written about.
To help beginners (and myself), I'm collecting my mistakes and also post my solution to it.
This post will probably grow as I progress myself

2) I want a complete n00b tutorial, as the other ones look cool, but too advanced at this moment (taking for granted some skills)

My first room was the "Your First Map"/"Getting started" from Valve. Same url as above.
Note: that wiki page of valve developer community seems to be usable to advanced mappers, so make a bookmark for future use.

You might not expect it, but I managed to b0rk the tutorial from Valve. I kept falling in eternity with some nice fading effects on spawning into the room.
Those error messages mean that the spawnpoint is inside a brush.
a) Check the spawnpoint on being a little bit above ground. See this thread specifically on spawnrooms: http://tf2maps.net/showthread.php?t=198
b) In my case I made a big brush (1024x1024x512) and then started to made the walls, roof and floor. So brushing a brush. As hammer can go inside brushes, I didn't noticed I was building inside my big brush. And then you can't spawn. Might be a typical mistake for ppl who used UnrealEd.